Comparative aggressiveness of Microdochium nivale and M. majus and evaluation of screening methods for Fusarium seedling blight resistance in wheat cultivars

Abstract

Microdochium majus and M. nivale are the primary agents of Fusarium seedling blight (FSB) of wheat in wet and cool crop growing regions. The differential responses and plant traits (root and stem length) of eleven wheat cultivars were evaluated using three inoculation methods with M. majus or M. nivale in soil, potato dextrose agar plate or detached leaf assay to develop a reliable screening method for the identification of resistance to FSB caused by Microdochium species in wheat. Microdochium nivale was the more aggressive FSB pathogen causing 30 % higher disease severity than M. majus and impacting significantly on root length and stem length. In contrast, M. majus was more pathogenic than M. nivale on wheat leaves reducing significantly the maximum efficiency of photosystem (PS) II (Fv’/Fm’). Fv’/Fm’ provides an estimate of the efficiency of PSII photochemistry (photosynthesis) at a given photosynthetically-active photon flux density defined as PSII operating efficiency if all PSII reaction centres were ‘open’. Regression analysis suggested that reduction in stem and/or root length and Fv’/Fm’ can be used as indicators of disease severity and for the detection of tolerance in wheat cultivars to specific diseases in the Fusarium complex. There were significant interactions between genotypes and species for the assessed disease and plant traits suggesting that resistance/tolerance mechanisms and genes maybe different to disease caused by individual Microdochium species. The most resistant cultivar to FSB identified consistently using all methods was Petrus, also known to be resistant to Fusarium head blight suggesting that this cultivar may possess useful durable resistance to more than one disease in the Fusarium disease complex.